System for generating discrete side-byside displays on a cathode ray tube



Dec. 12, 1961 w. ca. ALEXANDER EI'AL 3,

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAYTUBE Original Filed June 26, 1950 6 Sheets-Sheet 1 INVENTORS WILLIAM G.ALEXANDER CHARLES M=L HARDEN ATTORNEYS w. G. ALEXANDER ET AL 3,013,263SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE Dec. 12, 1961 DISPLAYS ON A'CATHODE RAY TUBE Original Filed June 26, 1950 6 Sheets-Sheet 2 522 6 iov a:

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ATTORNEYS Dec. 12, 1961 w. G. ALEXANDER ETAL 3,013,263

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAYTUBE Original Filed June 26, 1950 6 Sheets-Sheet 4 O A P On SPF-QMCOPOUJMm nZZOKhONJN W INVENTORS WILLIAM G.ALEXANDER CHARLES M=L. HARDENATTORNEY Dec. 12, 1961 we. ALEXANDER EIAL 3,013,263

SYSTEM FOR GENERATING DISCRETE SIDE-BY-SIDE DISPLAYS ON A CATHODE RAYTUBE Original Filed June 26, 1950 6 Sheets-Sheet 5 WILLIAM G. ALEXANDERCHARLES M L. HARDEN Dec. 12, 1961 w. G. ALEXANDER ETAL SYSTEM FORGENERATING DISCRETE SIDE-BY- ON A CATHODE RAY TUBE 3,013,263 SIDEDISPLAYS Original Filed June 26, 1950 6 Sheets-Sheet 6 h ad;

ATTORNE 5 Patented Dec. 12, 1961 3,613,263 SYSTEM FOR GENERATINGDISCRETE SmEdBY- SIDE DISPLAYS ON A CATHODE RAY TUBE William G.Alexander, El Cajon, Calif., and Charles McL.

Harden, Natick, Mass, assignors to The Bendix Corporation, a corporationof Delaware (Iontinuation of application Ser. No. 170,326, June 26,1950, now Patent No. 2,855,551, dated Gctoher 7, 1953. This applicationDec. 5, 1957, Ser. No. 700,876

8 Claims. (Cl. 343-11) This invention is a continuation of applicationSerial No. 170,326, filed June 26, 1950, now US. Patent No. 2,855,591.

This invention relates to indicator systems and more particularly to asystem for providing, on the face of a single cathode ray tube, a pairof simultaneous radar presentations each depicting the position of acommon target with respect to reference indicia, when scanned in arespective plane.

The invention has particular reference to Ground Controlled Approach orGCA systems in which an aircraft is guided to a landing under conditionsof poor visibility. In such systems as conventionally used, one or apair of radio pulse echo systems (radars) scan a region of spaceincluding the desired glide path. Two antennas are used, one scanningthrough a horizontal plane and the other scanning through a verticalplane. The antennas are oriented to pick up the target aircraft and thepilot is directed by radio communication to correct his flight path tobring it into coincidence with the desired glide path.

It has been customary, in the past, to present the indication from eachscan on a separate QR. tube, calling one the elevation presentation andthe other the azimuth presentation. The fact that each presentation wason a separate tube made it necessary that a separate observer besupplied for each presentation. This added to the expense of operatingthe system.

The presentations, as normally used, are sectors of a plan positionindication which have been distorted for more advantageous use. In theirusual form they could not be combined on a single cathode ray tube facewithout overlapping unless they were reduced in size to an undesirableextent.

It is an object of this invention to provide a system by which a pair ofradar presentations can be simultaneously shown on the screen of asingle cathode ray tube.

It is another object of the invention to provide a system by which apair of radar presentations of a combined size greater than that of thecathode my screen can simultaneously be shown on the said screen withouta substantial reduction of size.

It is a further object of the invention to provide a system by which apair of radar presentations may be combined on a single cathode rayscreen in such positions that they would normally overlap, byeliminating the overlapping portions of the presentations.

It is a still further object of the invention to simultaneously display,on a single cathode ray tube screen, a pair of sectorial plan positionindications of such size that they would normally overlap and to inhibitthe generation of those portions which would normally overlap.

A further object of this invention is to provide a combined azimuth andelevation GCA system operating in pulse to pulse alternation between theazimuth and elevation radiations and a corresponding range sweepalternation of the data utilization device.

The objects and advantages of the invention are realized by a system inwhich each plan position indication is developed in alternation with theother. The alternation occurs at the end of each line of the scan.Portions of the two indications which would overlap are electronicallyinhibited by the use of gates which are varied in duration as the scandevelops.

Referring now to the drawings:

FIG. 1 is a plan view of the screen of a cathode ray tube bearing a GCAelevation presentation;

FIG. 2 is a similar view of a screen carrying a GCA azimuthpresentation;

FIG. 3 is a similar view of a screen carrying both the presentations ofFIGS. .1 and 2, with portions in a region of overlap curtailed;

FIG. 4 is a schematic block diagram of a circuit embodying theinvention;

FIG. 5 is a schematic block diagram of a portion of the circuit of FIG.4;

FIG. 6 is a group of time related wave forms occurring in the circuit ofFIG. 5;

FIG. 7 is a schematic diagram of the circuit of FIG. 5;

FIG. 8 is a schematic circuit diagram of an angle data selector circuitforming part of the circuit of FIG. 4; and,

FIG. 9 is a schematic circuit diagram of a circuit for clipping theazimuth and elevation presentations to prevent overlap, this circuitlikewise being a part of the circuit of FIG. 4. i

Referring now more particularly to the drawing, FIG. 1 illustrates thecircular screen 10 of a cathode ray tube on which is displayed adistorted sector of a plan position indication generated by theelevation scanning antenna of a GCA installation. Displayed on thesurface of the screen, by some means other than the cathode ray'beam ofthe tube, is the outline of the pattern to which the indicationgenerated by the tube is made to conform. This pattern may bepermanently marked on the screen or may be projected on the screen froma source of visibleor invisible light or may be developed in any of anumber of known ways. It consists of a generally triangular outline 11conforming to the shape of a distorted sector of a plan positionindication, having its point of origin 12 at the left hand side of thescreen. A horizontal line 13 is also formed on the screen to representthe ground level to whichthe glide path is referred. The desired glidepath is indicated by a'line 14 which joins the ground line 13. near thepoint or origin 12, the point of juncture representing the point ofdesired touch down of an aircraft on the runway. Formed parallel to theglide path line 14 are a pair of dotted lines 15 which representreference distances from the glide path by which the error in elevationof a plane being guided can be visually determined. Such lines could,for example, indicate distances of 50 feet above and below the glidepath. Shown also in this figure are spaced vertical lincs16 which arerange marks having a spacing, for example, of One mile by which thedistances of the plane from the point of touch down can be seen at aglance. These range marks may be marked on the screen or may begenerated electronically by the cathode ray tube.

There is shown in FIG. 2 an indication 17 of the screen of a secondcathode ray tube bearing an indication of a second distorted sector of aplan position indication representative of the scan of the azimuthscanning antenna of the GCA system. The sector has its origin at thepoint 18 located at the top of the screen and has a triangularoutline-19, having a horizontal base at the bottom of this screen.Erected on the base is a vertical line 20 representative of a plan viewof the desired glide path as seen by a pilot of an approaching aircraft.A small rectangular representation 21 of the runway is formed at the topof the line 20. A pair of dotted lines 22 equally spaced on oppositesides of the line 29 provide reference indications of azimuthaldiscrepancies between the position of the planeand the glide path. Theselines can, for example, indicate distances of 50 feet on either side ofthe glide path.

Horizontally extending range marks 23 are also formed on thisindication, either electronically by means of the cathode ray means orby the same means as the remainder of the indication.

On each of the displays of FIGS. 1 and 2 the location of the aircraft isindicated by a luminous dot generated electronically by the cathode raybeam of the tube in response to the video signal of the radar set orsets used in the system.

GCA systems as known to the art may employ either one or two radar setsin connection with the scanning antennas. If one radar set is used, theset is connected alternatively to each of the two antennas. Thealternation may occur at the end of each scan or at the end f each lineof the scan. If two radar sets are employed each set may be continuouslyconnected to a respective one of the two antennas. In order to eliminatecross talk when the latter type of system is used, the antennas may bepulsed in alternation only one radar set being activated at a time.

The present invention is concerned with a means by which the twodisplays of FIGS. 1 and 2 may be combined on a single tube forobservation by a single observer Without overlapping of the displays andwithout reduction of their size to a point at which their legibility isimpaired. The invention is useable for GCA systems employing either oneor two radar sets and in which the antennas are activated sequentiallyat the termination at the end of each line. A combined display inaccordance with the invention is illustrated in FIG. 3. The screen ofthe tube is indicated at 26. The elevation display similar to that ofFIG. 1 appears in the upper half of the screen, while the azimuthdisplay similar to that of FIG. 2, but reoriented so that the glide pathnow lies in a horizontal direction, is formed on the lower half of thetube. The outlines 11 and 19 may be patterns formed by means other thanthe cathode ray beam of the tube to which the indications generated bythe cathode ray tube are caused to conform just as in the displays ofFIGS. 1 and 2. It will be noted that the lower portion of the elevationdisplay beneath the horizontal ground line 13 has been removed exceptfor a small portion 11 at the left hand edge of the display. It willalso be noted that the upper portion of the azimuth display has beenremoved, the display now terminating in its upper portion in ahorizontal line 27 which runs parallel to the ground line 13 of theelevation display.

With respect to all three figures, it will be understood that theindication generated by the cathode ray beam of the tube is that of theusual sectorial plan position indication distorted in a manner known tothe art to provide a more realistic indication to the observer. Thus, ineach indication the cathode ray beam at the beginning of each scan linestarts at the point of origin of the display such as point 12 in FIG. 1and point 18 in FIG. 2 and proceeds radially from that point for apredetermined length of time and then flies back to that point andbegins the generation of a second radially line displaced from the firstby a small angular amount. This action continues until the entiretriangular indication has been generated whereupon the generation of theindication is repeated. If during the generation of the indication anaircraft is encountered by the radiated beam, the cathode ray beam ofthe tube is intensified to produce a spot of light on the indicationrepresentative of the position of the aircraft at that instant.

The same manner of generation is followed in FIG. 3, the two indicationsbeing generated by alternate excursions of the cathode ray beam. Thisalternation occurs at the end of each line of each scan. The alternationoccurs so frequently that by' reason of the presistence of vision of thehuman eye, the two scans do not appear in alternation, but rather appearas a constant unflickering presentation as though both weresimulaneously and continuously present on the tube screen.

There is shown in FIG. 4 a block diagram of an entire GCA systemembodying the invention. The system includes an azimuth scanning antenna3%, the radiated beam of which has a cross sectional configuration asshown at 31 and scans in a horizontal path indicated by the line 32.Connected to this antenna, in the usual manner, for transmission andreception, is a radar transmitter and receiver 33 having a video outputterminal indicated at Z.

An elevation antenna is indicated at 34, the radiated beam of which hasa cross sectional configuration as indicated at 35 and scans in avertical path indicated by the line 36. To this antenna is connected, inthe usual manner for transmission and reception, a radio transmitter andreceiver 37. The receiver of this set is provided with a video outputterminal indicated at Y.

Both the scan paths 32. and 36 include the glide path down whichincoming aircraft are to be guided to a landmg.

A cathode ray tube 38 having a screen 26 is provided upon which thedisplay of FIG. 3 is to be presented. The cathode ray tube is providedwith horizontal deflection coils 39, 40 and vertical deflection coils41, 42 which operate in the usual manner. The tube is also provided witha cathode 43 and a pair of control grids 44 and 45. A horizontal drivercircuit 45 is provided which generates a current output having asaw-tooth waveform for deflecting the beam of the tube across the screenin a horizontal direction in a known manner. A clamp circuit 24 insuresthat the hon'zontal deflection voltage return to the same starting valueafter each sweep. The vertical driver circuit 47 performs the samefunction as circuit 46 with respect to vertical deflections of thecathode ray V. A clamp and cathode follower circuit 62 performsfunctions similar to circuit 24, as well as other functions which willbe described later. An intensifier circuit 49 is provided whichintensifies the cathode ray tube beam during each radial sweep to thepoint of producing a visible trace on the screen.

An azimuth video amplifier circuit 50 receives the video output of theradar set 33 by way of terminal Z and applies it to a video mixer 51.Here it is mixed with range marks generated in a manner to be laterdescribed and the output of the mixer is amplified in the video outputcircuit 52 and applied to the control grid 44 of the cathode ray tube.

An elevation video amplifier 53 receives the video output of radar set37 by way of terminal Y and after amplification applies it to the videomixer 51. The outputs of the amplifiers 50 and 53 are applied to thevideo mixer at diiferent times as will be explained hereafter.

A range mark generating system is also supplied. This includes a rangemark delay circuit 51 triggered by pulses from gate generator 60 bymeans of which the point of origin, from which the range marks aregenerated, can be adjusted manually as desired. This circuit provides avariable delay means which operates in a known manner to perform thisfunction. The output of the circuit controls the phase of range markoscillations produced in a range mark oscillator and shaper circuit 52.This circuit contains an oscillator producing an output having afrequency selected to result in the generation of range marks separatedby desired intervals, the usual interval being a mile. The output ofthis oscillator is clipped into a square wave form and utilized tosynchronize a range mark blocking oscillator 53. A range mark startingcircuit 54 is provided which initiates the action of the blockingoscillator 53. The output of the range mark blocking oscillator 53 isapplied to the video mixer 51 with the result that the output of thismixer consists of video signals received from the radar set 33 or 37combined with range marks.

The portion of the circuit of FIG. 4 which has been described above isof a conventional nature. The remainder of the circuit of this figurehas been added in accordance with the invention in order to provide forthe simultaneous display of azimuth and elevation information on thescreen 26. In order to accomplish this result, it is necessary that theazimuth and elevation displays be generated in alternation. In order togenerate such displays in alternation, switching arrangements must beprovided so that, for example, when the elevation display is beingapplied to the screen, each line of the scan will start from the pointof origin which has been selected for that display and which isdifferent from the point of origin selected for the azimuth display.There likewise must be utilized video information coming from the radarset 37 and angle data voltage related to the position of the elevationantenna 34.

There are two possible methods of generating side-byside displays, inthe first of which the displays are generated in alternation after eachscan line, thus one line of the scan of the elevation antenna will begenerated and then a line of the scan of the azimuth indication will begenerated. The other alternative is to generate the entire elevationscan and then generate the entire azimuth scan. The present invention isdirected to systems in which the alternation occurs after each line ofthe scan.

Thus, following the generation of one line of the elevation scanutilizing the elevation video information and angle data voltage, it isnecessary that the system now be switched to receive only data from theradar set 33 and the azimuth antenna 3th. This switching between azimuthand elevation data must occur at the pulse repetition frequency utilizedby the radar sets. For purposes of illustration, we may assume that thisfrequency is 2400 cycles per second.

The system as shown in FIG. 4 includes an electronic selector switch 55which performs several of the switching functions referred to above.This switch is triggered by a system trigger generated elsewhere in thesystem and recurring 2400 times per second. The switch generatestriggers which are applied by conductors 56 and 57 to the transmitter ofthe azimuth radar set 33 and the transmitter of the elevation radar set37 respectively. These triggers are separated by time intervals ofapproximately 215 micro-seconds. These triggers are also supplied byconductors 58 and 59 to a gate generator of which generates a series ofsquare gating pulses that are applied to various parts of the circuit ina manner to be described later.

The selector switch 55 also performs the function of alternatelyswitching the video input to the cathode ray tube from that supplied byradar set 33 to that supplied by radar set 37 and back again. In orderto perform this function the selector switch generates gates which occurin alternation and each of which is supplied to a respective one of thevideo amplifiers 50 and 53 so that these amplifiers are gated into aconductive state in alternation.

In connection with the azimuth and elevation scanning antennas there areproduced a pair of voltages which vary as a function of theinstantaneous scanning position of the respective energy beams emittedfrom these antennas. These antennas may each comprise a linear array ofdipoles mounted on a variable width wave guide as described in volume26, entitled Radar Scanners and Radomes of the Radiation LaboratorySeries, published 1948 by McGraw-Hill Book Company, Inc., New York City.The description will be found on pages 185-193 inclusive. The width ofthese antennas is cyclically and synchronously varied to produce thescanning of their beams. This width varying means may, by a simplemechanical linkage, be caused to vary the setting of a pair ofpotentiometers to produce the pair of voltages referred to. Thesevoltages are used to modify the vertical deflection current applied tothe coils 41 and 42 in order that distortion of the display may besecured in order to produce the presentations in the manner illustrated.These voltages are also employed to clip the presentations through theuse of gating voltages in order that the two displays may be applied tothe same cathode ray screen in the manner illustrated in FIG. 3. Inorder to carry out these functions the electronic selector switch 55produces a pair of gating voltages which are applied to an angle dataselector 61, the output of which is applied to the clamp and cathodefollower circuit 62. The angle data selector receives input voltage fromthe antennas 3t and 34 by way of conductors 63 and 64. The gatesdeveloped by the switch 55 determine which of these input voltages is tobe utilized at a given time since they also are employed in alternation.A map clipper 65 is employed to generate the necessary gating voltagesfor clipping the azimuth and elevation displays as illustrated in FIG.3. This circuit receivers an input from the angle data selector 61 ofthe angle data passed by that circuit and also receives gating voltagesfrom selector switch 55.

In order to establish the respective points of origin of the azimuth andelevation displays, a pair of centering circuits are employed, eachestablishing one component of the points of origin of these displays.The centering circuit related to the horizontal deflection systemcomprises a triode 66, the anode of which is connected by way of aresistor 67 to the coil 39 of the horizontal deflection system. Thecontrol electrode of this tube receives gating voltage from the selectorswitch 55 by way of a conductor 63. The centering system relating to thevertical deflection system comprises a triode 70, the anode of which isconnected by way of a resistor 71 to the coil 41 of the veiticaldeflection system. The control electrode of this tube receives gatingvoltage from the selector switch 55 by way of a conductor 72.

The make-up and functioning of the electronic selector switch 55 is morefully set forth in FIGS. 5, 6 and 7. FIG. 5 is a block diagram of theswitch, while FIG. 6 illustrates the waveforms at different points ofthe circuit of FIG. 5. The waveforms are identified by block letters inFIG. 6 and the points where they are found in FIG. 5 are likewiseindicated by the use of the same letters. The basic element of theswitch is a multivibrator circuit 73, having a 50% duty-cycle, thecomplete cycle occupying a time of approximately 430 microseconds. Thesystem trigger is applied to the input of this circuit from the terminalX. This trigger has a waveform such as shown at A in FIG. 6. It can beseen that this waveform comprises a series of positive impulsesseparated by time intervals of 430 micro-seconds. The output of themultivibrator 73 is taken at two points, differentiated and applied asthe waveforms B and C to the inputs of two isolation amplifiers 74 and75. Wave forms B and C are seen to be the clifierentiated products ofthe output of a multivibrator having a 50% duty-cycle. Each waveformconsists of a series of impulses of alternate polarity, impulses ofpositive polarity being produced at the leading edge of the positiveportion of the multivibrator waveform and impulses of negative polaritybeing produced at the leading edges of the negative portions of themultivibrator waveform. The impulses of the two waveforms are reversedin polarity. The isolation amplifiers 74 and 75 eliminate thenegative-going impulses and amplify the positive-going impulses of thesewaveforms to produce output waveforms D and E. These two waveforms areapplied as triggering voltages to the transmitters of radar sets 33 and37 and to the gate generator 6t) as described above in connection withFIG. 4. These waveforms are also utilized as triggering voltages in twomicro-second multivibrators 76 and '77. The outputs of thesemultivibrators are the waveforms F and G which are seen tov be squarepulses of 80 microseconds duration, separated by time intervals of 430micro-seconds. The pulses of each of these waveforms occur midway of thepulse intervals of the other.

One of the two multivibrators 76 and 77 may be identically duplicated inthe gate generator 6%, since the output of that generator is a waveformidentical with the sum of F and G. If desired, the multivibrators 76 and77 may be utilized as the gate generator 60 with appropriate outputleads to the various elements of FIG. 4 which are shown as receiving the80 micro-second pulse output of generator 60. For clarity, however, aseparate gate generator 60 has been illustrated in FIG. 4. The outputsof the multivibrators 76 and 77 are applied to respective isolationamplifiers 78 and 79. The output of these amplifiers is applied to themap clipper :ircuit 65 which will be later described.

The output waveform F from multivibrator 76 is also differentiated toproduce the waveform H which is applied to the input of a 215micro-second multivibrator 86 From this circuit two waveforms J and Kare recovered, these being taken from points of opposing polarity in theoutput circuit of the multivibrator. As will be seen, these waveformsconsist of square waves having alternating, positive and negative-goingportions of 215 micro-seconds duration. The positive portions of thesewaveforms are utilized as gates for various parts of the circuit of FIG.4. It will be noted that these positive portions occur in the twowaveforms in alternation. They are amplified in gate amplifiers 81 and82 before use. The waveforms J and K are applied to the angle dataselector 61 in which circuit they are utilized in a manner to be laterdescribed. The waveform I is also applied to the control electrodes ofcentering tubes 66 and 76 which have been previously described. Theapplication of this waveform to these tubes causes the conductionthereof to be shifted between two different levels, one level occurringduring the application of data relating to the elevation presentation tothe cathode ray tube and the other level occurring during thepresentation of data relating to the azimuth presentation.

Turning now to FIG. 7, we find that the multivibrator 73 comprises thetwo tubes 85 and 86 and their associated circuit elements. The waveformA is applied from terminal X to the control electrode of tube 85 whichis normally in a non-conducting state. The positive impulses of thiswaveform trigger the multivibrator by causing the tube 85 to conduct.Once this action has been started, the waveform A synchronizes theaction of the multivibrator to its recurrence. The waveform B consistsof the impulses of waveform A, plus negative-going impulses derived fromthe control grid of tube 85. When this tube ceases to conduct at thechange-over point of the multivibrator action, the negative-goingimpulses are derived by differentiation of the control electrode voltagein the network composed of condenser 87 and resistor 88. This waveformis applied to the control electrode of a tube 89 which is a part ofisolation amplifier 74. The waveform C is derived from the anode of tube85 by differentiation of the leading edges of the excursions of themultivibrator output. This differentiation occurs through a networkcomposed of condenser 90 and resistor 91 and the resulting waveform isapplied to the control electrode of a tube 92 which, with its circuitelements, comprises isolation amplifier 75.

The waveforms D and E are derived from the cathodes of tubes 89 and 92respectively, from whence they are applied to the transmitters of radarsets 33 and 37 and to the input circuits of multivibrators 76 and 77.Multivibrator 76 is composed of tubes 93 and 94 and their associatedcircuit elements and multivibrator 77 is composed of tubes 95 and 96 andtheir associated elements. The waveform D is applied to the controlelectrode of tube 93 and the Waveform E is applied to the controlelectrode of tube 95.

The waveform F is derived from the anode circuit of tube 94 ofmultivibrator 76 and the waveform G is derived from the anode circuit ofthe tube 95 of the multivibrator 77. The waveform F is applied to thecontrol electrode of tube 97 which, with its circuit elements,constitutes the isolation amplifier 78 and the waveform G is applied tothe control electrode of the tube 98 which is a part of the isolationamplifier 79. Outputs from the cathodes of these tubes are available asgating voltages and are utilized for this purpose in the map clippercircuit 65.

The waveform H is derived from a variable tapping point on a resistor 99in the anode circuit of tube 93. The voltage from this point isdifferentiated through a network consisting of condenser 16% andresistor 101, and is applied to the control electrode of a tube 102which, with a tube 183 and their associated circuit elements, comprisesmultivibrator 81 From the anode circuit of tube 102 is derived thewaveform K, while the waveform J is taken from the anode circuit of tube103. These Waveforms are applied to the respective control electrodes oftwo tubes 184- and 105 which respectively, with their associated circuitelements, constitute gate amplifiers 81 and 82. From the cathodecircuits of these tubes the Waveforms J md K are available and aresupplied to the necessary elements of the circuit of FIG. 4.

The schematic circuit diagram of the angle data selector 61 isillustrated in FIG. 8. In that figure we find a pair of terminals M6 and107 across which azimuth angle voltage from the azimuth scanning antenna39 is applied to the anodes of a pair of clamping tubes 108 and 109through a pair of resistor 110 and 111. Voltage of the waveform K isapplied from terminal 112 to the control electrodes of these tubes.Across a second pair of terminals 113 and 114 elevation angle voltagefrom elevation scanning antenna '34 is applied through resistors 115 and116 respectively, to the anodes of two clamp tubes 117 and 118. Voltageof the waveform J is applied to the control eelctrodes of these tubesfrom terminal 119. The control grids of tubes 117 and 118 are connectedthrough a resistance network to a source of negative voltage representedby terminal 120. This source establishes a bias on these grids, ofsulficient magnitude to render the tubes non-conductive in the absenceof a positive voltage applied to the control grids. On the other hand,the tubes 108 and 169 are conducting in the absence of a negativevoltage applied to their control grids.

A pair of tubes 121 and 122 have their cathodes directly connected andconnected through a resistance network to the terminal 121}. The controlelectrode of tube 121 is connected to the anode of tube 108 acrossresistor 110 and the control electrode of tube 122 is connected in thesame manner to the anode of tube 117 across resistor 116. An outputterminal 123 is dierctly connected to the cathodes of these tubes.

A pair of tubes 124 and 125 have their cathodes directly connected andconnected through a resistive network to the terminal 128. The controlelectrode of tube 124 is connected to the junction between the anode oftube 109 and resistor 111 and the control electrode of tube 125 isconnected to the junction of the anode of tube 118 and resistor 115. Aterminal 126 is directly connected to the cathodes of these tubes.

In the operation of this circuit the tube 108 is normally heavilyconducting. The application of the negativegoing excursion of thewaveform K to its control grid is suflicient, however, to cut-oifconduction therein. So long as tubes 1118 and 1119 are conducting, theiranode voltage, applied to the control grids of tubes 121 and 124, issuificient to render these tubes non-conducting so that the applicationof azimuth angle voltage to the terminals 166 and 197 is ineffective toproduce an output at the terminals 123 and 126. Due to the reversedpolarity of the waveforms I and K at the times when tubes 108 and 109are conducting and no azimuth angle voltage may, therefore, be derivedfrom terminals 123 and 126, a negative-going excursion of the waveform Iis being applied to the control electrodes of tubes 117 and 118. This,in conjunction with the application of biasing voltage from the terminal120, maintains these tubes in a non-conductive state so that elevationangle voltage be ing applied across terminals 113 and 114 is effectively9 applied to the control electrodes of tubes 122 and 125 causing thosetubes to conduct. Since the terminals 123 and 126 are directly connectedto the cathodes of tubes 122 and 125 elevation angle voltage isavailable across terminals 123 and 126.

Now as soon as a negative-going excursion of the'waveform K is appliedto the control grids of tubes 16S and M9, conduction in these tubes iscaused to cease, with the result that the tubes 121 and 124 are nowrendered conductive and azimuth angle voltage is therefore appliedacross the terminals 123 and 126. At the same time a positive-goingexcursion of the waveform J is being applied to the control electrodesof tubes 117 and 118, with the result that these tubes are now renderedconductive and by their conduction render tubes 122 and 125non-conductive. During this period of time, therefore, no elevationangle voltage is applied across terminals 123 and 126.

it can thus be seen that elevation angle voltage and azimuth anglevoltage are alternately available from the output of this circuit duringsuccessive periods of 215 micro-seconds each.

FIG. 9 shows a schematic diagram of the map clipper 65 and of the clampand cathode follower circuit 62 and the vertical driver circuit 47. Theclamp and cathode follower circuit comprises a cathode follower circuitutilizing a tube 127, the output of which is taken from its cathode andsupplied through a potentiometer 123 tothe control electrode of tube131), forming a part of the vertical driver circuit. Angle data voltagefrom the angle data selector 61 is supplied to the control electrode oftube 127 by way of a terminal 129. A clamp tube 155 has its anodeconnected to the control grid of the tube 136' and receives pulses fromthe gate generator oil by way of terminal 156.

The tube 13a is connected for operation as a relaxation oscillator withan output which has a saw-tooth waveform. To this end the anode isconnected to B+ through an inductance 157 and a feedback path from theanode to the control grid is provided by way of a resistor 158 andcondenser 159. The output voltage of this circuit is the verticaldeflection voltage applied to the vertical deflection coils 41 and 42 ofthe cathode ray tube. It is also utilized in the map clipping circuit ina Way to be described.

The tube 130 can only be rendered conductive during the receipt of agating impulse from the gate generator 60 by way of clamp tube 155 andthe time constants of the circuit 47 are such that each saw-tooth of itsoutput occupies the whole duration of the gating impulse, the controlgrid of the tube 130 being returned by the clamp tube 155 to a fixedreference voltage at the end of. each gating impulse. The angle datavoltage applied by the cathode follower 127 governs the amplitude of theoutput saw-tooth of circuit 47.

The output of the circuit 47 is shown as a negativegoing saw-toothexcursion 131 which is applied by way of a condenser 132 to a resistor133. This resistor is connected as a potentiometer to the control gridof amplifier tube 134. The waveform of the voltage applied to this gridby way of the potentiometer is indicated at 135. The cathode of thistube is connected by way of a potentiometer 136 to a source of negativevoltageindicated by the terminal 137. This tube will conduct during the:initial portion of the Waveform 135 depending upon the setting of thepotentiometer 133. The final portion of the waveform 13$ will, however,cause thetube to be cut-off with the result that an output waveform, asindicated at 138, will be produced. This output will have the form of asubstantially square topped, positive-going pulse. The duration of thispulse is seen to be dependent upon the amplitude of the negative-goingsaw-tooth 131 which is governed by the angle data voltage. The terminaledge of the pulse 138 is fixed, so that an increase ins the amplitude ofthe waveform 131 will result in'the lead The pulse is differentiated inthe network comprising a condenser 139 and a resistor 141 to produce aresulting waveform of the type shown at 141 which is applied to thecontrol grid of a pentode coincidence tube 14-2. This tube is normallyin a non-conducting state due to the application of a negative voltagefrom a source indicated by a terminal 143 through the resistor w thecontrol grid. The suppressor grid of tube 142 is connected by a resistor144 to ground. Negative voltage is supplied by way of a terminal 145through a resistor 146 to the junction of resistor 144 and th esuppressor grid. Likewise applied at this point is the waveform G whichis applied from the selector switch 55 by way of a terminal 147 througha resistor 148. The tube 142 is normally biased so heavily that itrequires the coincidental application of the positive-going spike of thewaveform 141, and a positive-going excursion of the waveform G to renderit momentarily conducting. When this occurs a negativegoing spike, asindicated at 149, will be applied to the input circuit of a one shotmultivibrator 150. This multivibrator comprises a pair of tubes 151 and152. The control grid of tube 151 is connected to B+ through a resistor153 of such value that this tube is normally conducting and tube 152 isnormally non-conducting. The application of the negative-going spike 149to the control grid of tube 151 triggers the multivibrator through onecycle of its operation, whereupon it returns to its initial conditionand remains in that state until the receipt of another negativetriggering spike. Output from the multivibrator 151) is taken from theanode of tube 152 at terminal 154 and is applied by way of conductor 48to the electrode 45 of the cathode ray tube 38, as shown in FIG. 4. Itcan be seen that this voltage, in the normal state of the multivibrator150, will be a positive voltage. Upon the application of the negativetrigger 149, the multivibrator will generate a negative-going voltage excursion which will have a duration dependent upon the time constants ofthe multivibrator circuit.

The portion of the map clipping circuit which has been described is thatwhich performs the function of clipping the azimuth presentation whichis the lower presentation of FIG. 3. It can be seen from that figurethat it is necessary to clip the upper portion of the presentation alonga horizontal line. This is accomplished through the effect of the angledata voltage, the gate impulses from gate generator 60, and the waveformG upon the circuit described above. The application of waveform G to thesuppressor grid of tube 142 insures that that tube can conduct onlyduring those times when angle data voltage from the azimuth antenna isavailable from the angle data selector 61. The angle data voltageapplied by way of terminal 129 and tube 127 regulates the amplitude ofthe saw-tooth waveform 131 in the manner described, so that theamplitude of that waveform is a function of the instantaneous scanningposition of the energy beam from the aximuth an-. tenna, with theamplitude of the waveform increasing as the antenna scans from left toright as Viewed by an incoming pilot. Until the scan position has movedto a point several degrees to the right of the horizontal base line ofthe azimuth scan, the amplitude of the waveform 131 is too small tocause the production of a pulse 138 in the output of the tube 134 andthus, the multivibrator is not triggered and no clipping occurs. As thescan position reaches this point, however, the amplitude of thewaveform- 131 has increased to an amount suflicient to begin with aproduction of pulses 138 in the output of tube 134. Thus the circuitbegins to clip the upper portion of the presentation near the right handedge of the cathode ray screen. As the beam swings further to the right,the amplitude of the waveform 131 increases and the leading edge of thepulse 138 occurs progressively earlier in time with the result thatclipping now occurs sooner in the duration of each radial trace of thebeam of the cathode ray tube. With the proper control of the variationof the amplitude of the waveform 131, as the antenna beam swings to theright, the line 27 marking the upper boundary of the azimuth scan may bemade to be horizontal.

We come now to the portion of the map clipper which eiiects the clippingof the elevation presentation or the upper presentation of FIG. 3. Thisportion of the circuit includes a multivibrator 160 of the one shot typewhich, on being triggered, generates a positive pulse 161 ofapproximately micro-seconds duration and then reverts to its quiescentstate until it is again triggered. This multivibrator comprises a pairof tubes 162 and 163. System triggering voltage of negative polarityresembling the waveform A is applied to the control grid of tube 162 byway of terminal 164. Elevation gating voltage of the waveform F isapplied to the anodes of the multivibrator tubes through resistors 165and 166 respectively, by way of terminal 167. An amplifier 168 isprovided having its anode connected to the anode of tube 162 and itscathode connected to ground by way of a variable tap on a resistor 169.Positive voltage from a source 3-! is applied to the cathode by way ofterminal 170 and resistor 171. Elevation angle data voltage is appliedto the control grid of tube 168 by way of the terminal 172. The anode oftube 162 is connected to a source of negative voltage through acondenser 173 and a resistor 174 by way ofa terminal 175. r

The multivibrator 160 is not operative in the absence of a positivegating voltage of waveform F. When this voltage is applied to the anodesof the multivibrator tubes, the multivibrator is in its quiescent state.The application of the negative system trigger voltage to the controlgrid of tube 162 would result in the triggering of the multivibrator ifit were not for the presence of the tube 163. When the elevation antennabeam is in the above ground portion of its scan the elevation angle datavoltage applied to the grid of tube 168 causes that tube to conductsufficiently to maintain the anode voltage of tube 162 at a value suchthat the negative system trigger applied to its control grid cannot beamplified and the multivibrator fails to respond to that stimulus. When,however, the elevation antenna scan moves to a position below the groundlevel the elevation angle data voltage is reduced until the tube 168nears the point of out-01f. 'In this condition the anode voltage on thetube 162 is high enough in the presence of the waveform F to respond tothe system trigger and to generate its output pulse 161. This is appliedthrough a variable tap on resistor 165 and by way of a condenser 176 tothe control grid of tube 151 of multivibrator 156. The trailing edge ofthis pulse triggers the multivibrator 150 into its unbalanced state. Itcan thus be seen that during the duration of the positive-goingexcursions of the waveform F, the multivibrator 160 is activated butunable to respond to the system trigger until the scan position of theelevation antenna moves below ground. At this time the multivibratorresponds to the system trigger to generate the pulse 161. This pulse isof sufiicient duration to allow the generation of the portion 11 of theelevation presentation shown in the upper part of FIG. 3. The trailingedge of this pulse initiates the output pulse of the multivibrator 150which blanks the cathode ray tube for the duration of the sweep of eachsweep of the cathode ray beam following the termination of the pulse161,

To summarize the operation of the entire system depicted in FIG. 4, wehave a pair of antennas scanning a common region containing a glide pathdown which aircraft are to be guided to a landing. The azimuth antenna36 base directive beam 31 scanning along the 12 horizontal path 32. Theelevation scanning 34 has a directive beam 35 scanning vertically alonga path 36. The azimuth and elevation antennas are connectedrespectively, to two radar sets 33 and 37.

An electronic selector switch 55 is provided which responds to a systemtrigger, consisting of an impulse generated at regular intervals of 430micro-seconds, to generate various output impulses. It generates twotriggering voltages of the waveforms D and E corresponding in form tothe Waveform of the system trigger A, but with the impulses of onewaveform occurring midway of the intervals between the impulses of theother. These impulses are utilized to trigger the two radar setsalternately into activity, a single radar pulse being transmitted uponthe receipt of each trigger. The same triggering voltages are alsoapplied to a gate generator 60 which generates an micro-secondpositive-going impulse upon the receipt of each trigger. These 80micro-second impulses are utilized in several portions of the circuit.They activate a range mark generating circuit. They also activatehorizontal and vertical drivers which generate deflection voltages forthe deflection circuits of a cathode ray tube 38. They are also appliedto an intensifier circuit which causes the generation in the cathode raytube of a beam of sufficient intensity to produce a visible trace on thetube screen for the duration of the impulse.

The video output of the radar receivers of sets 33 and 37 are appliedrespectively to azimuth and elevation video amplifiers 5t) and 53. Theseamplifiers are also activated in alternation by 215 micro-secondimpulses generated by the selector switch 55. This alternate activationrenders each amplifier active at a time when its respective radar set istransmitting a pulse and receiving video information from any targetswhich may be present. The output of these amplifiers is mixed with therange marks generated by the range mark generating circiut and appliedto the cathode ray tube. The waveform J is also applied to the controlgrids of two centering tubes 66 and 70 which operate on the twodeflection circuits and, by virtue of the alternating levels of thewaveform 1, cause the two displays on the tube screen to be generated atdifferent locations on the screen.

Angle data voltage is also generated by each of the antennas 3t) and 34and used to control the clipping of the two presentations in order thatthey may be displayed on the screen in as large a size as possiblewithout overlapping at their adjacent edges. To perform this function anangle data selector 61 and a map clipper circuit 65 are provided. Theangle data selector is controlled by the two waveforms J and K andthereby caused to alternately present in its output angle data voltagefrom each of the two antennas. This alternation is in synchronisrn withthe activation of the two video amplifiers and the two centering tubes66 and 70, in order that everything pertaining to each respectivepresentation be segregated into respective alternating time intervals.The map clipper 65 receives voltages of the two waveforms F and G andthe elevation trigger voltage of waveform D from the selector switch 55.It also receives angle data voltage from the angle data selector 61 andhas applied to it the output of the vertical driver 47. From theseinputs it generates gating voltages appropriate to each presentationduring the time intervals when that presentation is being generated andclips each respective presentation along the portion of its boundarywhich is adjacent to the other presentation and would otherwise overlap.

It should be understood that the values of voltages and times that havebeen given herein are for the purpose of illustration only and are notto be considered as restrictive of the invention.

What is claimed is:

1. A radio pulse echo system comprising radio transmitting and receivingmeans, a pair of directive antennas, each scanning a respective sectorof space, a cathode ray tube, means generating a pair of voltages eachvarying in accordance with the scan of a respective one of saidantennas, means impressing on each antenna in alternation a pulse ofradio frequency energy, and means generating on said cathode ray tube adiscrete plan position indication of the output of said system asderived from each of said antennas, said indication generating meanscomprising means repetitively generating a saw-tooth output voltage insynchronism with the emission of said pulses, means responsive to saidoutput voltage for repetitively deflecting the ray of said cathode raytube in synchronism therewith, switching means applying said pair ofvoltages to said saw-tooth voltage generator in alternation insynchronism with said pulses to vary the amplitude of said outputvoltage in accordance therewith, means generating a biasing voltagealternating between two values in synchronism with said pulses .andmeans applying said biasing voltage to said deflecting means toalternate the starting point of said deflections of said cathode raybeam between two locations.

2. A radio pulse echo system comprising radio transmitting and receivingmeans, a pair of directive antennas, each scanning a respective sectorof space, a cathode ray tube, means generating a pair of voltages eachvarying in accordance with the scan of a respective one of saidantennas, means impressing on each antenna in alternation a pulse ofradio frequency energy, and means'generating on said cathode ray tube adiscrete plan position indication of the output of said system asderived from each of said antennas, said indication generating meanscomprising means repetitively generating a saw-tooth output voltage insynchronism with the emission of said pulses, means responsive to saidoutput voltage for repetitively deflecting the ray of said cathode raytube in synchronism therewith, switching means applying said pair ofvoltages to said saw-tooth voltage generator in alternation insynchronism with said pulses to vary the amplitude of said outputvoltage in accordance therewith, means generating a biasing voltagealternating between two values in synchronism with said pulses and meansapplying said biasing voltage to said deflecting means to alternate thestarting point of said deflections of said cathode ray beam between twolocations, said switching means comprising: a first pair of electrondischarge tubes each having an anode, a cathode and a control electrode,said tubes having their cathodes directly connected and connected to oneside of said translation channel, a second pair of electron dischargetubes each having an anode, a cathode and a control electrode, saidtubes having their cathodes directly connected together and to theremaining side of said translation channel, a first pair of clampingdevices, each having an input and an output circuit, means can nectingthe output circuit of each of said clamping devices to the controlelectrode of a tube of a respective one of said pairs of tubes, a secondpair of clamping devices, each having an input and an output circuit,means connecting the output circuit of each of said clamping devices tothe control electrode of the remaining tube of a respective one of saidpairs of tubes, means rendering said pairs of clamping devicesconductive and non-conductive in alternating periods of equal durationsynchronized with said pulses, the devices of each pair being conductivewhen those of the other pairs are non-conductive and means coupling arespective voltage of said pair of voltages across the output circuitsof each pair of said clamping devices. a

3. A radio pulse echo system comprising radio transmitting and receivingmeans, a pair of directive antennas, each scanning a respective sectorof space, a cathode ray tube, means generating a pair of voltages eachvarying in accordance with the scan of a respective one of saidantennas, means impressing on each antenna in alternation a pulse ofradio frequency energy, and means generating on said cathode ray tube adiscrete plan position indication of the output of said system asderived from each 14 of said antennas, said indication generatingmeanscomprising means repetitively generating a saw-tooth output voltage insynchronism with the emission of said pulses, means responsive to saidoutput voltage for repetitively deflecting the ray of said cathode raytube in synchronism therewith, switching means applying said pair ofvoltages to said saw-tooth voltage generator in alternation insynchronism with said pulses to vary the amplitude of said outputvoltage in accordance therewith, means generating a biasing voltagealternating between two values in synchronism with said pulses and meansapplying said biasing voltage to said deflecting means to alternate thestarting point of said deflections of said cathode ray beam between twolocations, said switching means comprising: means generating a pair ofsquarewave voltage outputs with the positive-going excursions of each ofsaid outputs coinciding in time with the negative-going excursions ofthe other, a first pair of electron discharge tubes each having ananode, a cathode and a control grid, the cathodes of said tubes beingdirectly connected, means connee ting said cathodes to one side ofsaidtranslation channel, a second pair of electron discharge tubes eachhaving an anode, a cathode,'and a control electrode, the cathodes ofsaid tubes being directly connected, means connecting said cathodes tothe other side of said translation channel, a first pair of clampingdevices each having an input and an output circuit and being soconnected as to be normally conductive, means impressing on said inputcircuits one of said squarewaves outputs, means connecting the outputcircuit of each of said devicesto the control electrode of'a tube of arespective one of said pairs of tubes, means coupling one of said pairof varying voltages across the output circuits of said first pair ofclamping devices, a second pair of clamping devices each having an inputand an output circuit and being so connected as to be normallynon-conductive, means impressing on the input circuits of the last nameddevices the other of said squarewave outputs, means connecting theoutput circuit of each of the last named devices to the controlelectrode of the remaining tube of a respective one of said pairs oftubes, and means coupling the remaining one of said pair of varyingvoltages across the output circuits of said second pair of clampingdevices.

4. A system for producing a multiple display on a cathode ray tube ofthe outputs of a pair of radio pulse echo systems scanning throughindividual sectors of space, comprising, means triggering said radioecho systems to produce pulses of energy in sequential alternation,means deriving from each of said systems an angle voltage theinstantaneous magnitude of which is representative of the position ofthe beam of the system in its scanning pattern, a pair of quadraturelyacting cathode beam deflecting means for said cathode ray tube, meansoperating on said deflecting means to shift the cathode beam of saidcathode ray'tube between two starting positions on the screen thereof insynchronism with the alternation of said pulses of energy, meansgenerating and applyingsweep voltages to both of said deflecting meansin synchronism with said pulses of energy, and means varying themagnitude of the sweep voltage applied to one of said deflecting meansin sequential altemation, between values which are functions of therespective angle voltages of said radio echo systems, said sequentialalternation being in synchronism with the sequential alternation of thetriggering of said radio echo systems.

5. In a ground controlled approach system of the character described, anazimuth antenna, an elevation antenna, means exciting said antennas inalternation to transmit a pulse of energy, whereby there are producedazimuth and elevation energy beams in alternation, means scanning eachof said antenna beams in space, means deriving a corresponding azimuthangle voltage and an elevation angle voltage the instantaneous magnitudeof each of which is representative of the position of the respectivebeams, a cathode ray tube having a pair of quadraturely screen of saidcathode ray tube in synchronism with the iransmission of successive onesof said pulses of energy, a. pair of sweep generating means operatedsynchronously with said transmitting means, each of said sweepgenerating means energizing a respective one of said deflecting means, apair of sweep voltage generating channels in one of said sweepgenerating means, means energizing one of said channels to produce asweep voltage in syn- :hronism with the transmission of said energypulses forming said azimuth beam, means energizing the other of saidchannels to produce a sweep voltage in synchronism with the transmissionof said energy pulses forming said elevation beam, means applying saidazimuth angle voltage to said one channel to control the magnitude ofthe sweep voltage produced thereby, means applying said elevation anglevoltage to the said other of said channels to control the magnitude ofthe sweep voltage produced thereby, and means combining outputs of saidchannels of said second sweep generating means to produce a sweepvoltage with sequentially alternating amplitudes varying in accordancewith the position of said antenna beams in space.

6. A system for producing a multiple display on a cathode ray tube ofthe outputs of a pair of radio pulse echo systems scanning throughindividual sectors of space, comprising: means triggering said radioecho systems to produce pulses of energy in sequential alternation,means deriving from each of said systems an angle voltage theinstantaneous magnitude of which is representative of the position ofthe beam of the system in its scanning pattern, a pair of quadraturelyacting cathode beam deflecting means for said cathode ray tube, meansoperaton said deflecting means to shift the cathode beam of said cathoderay tube between two starting positions on the screen thereof insynchronism with the alternation of said pulses of energy, one of saidcathode beam deflecting means being operable to deflect said cathodebeam along a time base coordinate and the other being operable todeflect said cathode beam along an expansion coordinate, meansgenerating and applying sweep voltages to both of said deflecting meansin synchronism with said pulses of energy, and means varying themagnitude of the sweep voltage applied to said expansion coordinatedeflecting means in sequential alternation, the variation of saidmagnitude alternating as a function of the respective angle voltages ofsaid radio echo systems, said sequential alternation being insynchronism with the sequential alternation of the triggering of saidradio echo systems.

7. In a ground controlled approach system of the character described, anazimuth antenna, an elevation antenna, means exciting said antennas inalternation to transmit a pulse of energy, whereby there are producedazimuth and elevation energy beams in alternation, means scanning eachof said antenna beams in space, means deriving a corresponding azimuthangle voltage and an elevation angle voltage the instantaneous magnitudeof each of which is representative of the position of the respectivebeams, a cathode ray tube having a pair of quadraturely acting cathodebeam deflecting means, means operable upon said beam deflecting means toposition said cathode beam in one starting position on the screen ofsaid cathode ray tube coincident with the transmission of each of saidpulses of energy from said 16 azimuth beam transmitting means and toposition said cathode beam in another starting position on said screenof said cathode ray tube coincident with the transmission of each ofsaid pulses of energy from said elevation beam transmitting means, oneof said cathode beam deflecting means being operable to deflect saidcathode beam along a time base coordinate and the other being operableto deflect saidtcathode beam along an expansion coordinate, a firstsweep generating means operable to energize said time base cathode beamdeflecting means, a second sweep generating means operable to energizesaid expansion cathode beam deflecting means, means energizing saidfirst sweep generating means to produce a sweep voltage in synchronismwith the transmission of each of said pulses of energy, a pair of sweepvoltage generating channels in said second sweep generating means, meansenergizing one of said channels to produce a sweep voltage insynchronism with the transmission of energy pulses forming said azimuthbeam, means energizing the other of said channels to produce a sweepvoltage in synchronism with the transmission of pulses forming saidelevation beam, means applying said azimuth angle voltage to said onechannel to control the magnitude of the sweep voltage produced thereby,means applying said elevation angle voltage to the said other of saidchannels to control the magnitude of the sweep voltage produced thereby,and means combining outputs of said channels of said second sweepgenerating means to produce a sweep voltage with sequentiallyalternating amplitudes varying in accordance with the position of saidantenna beams in space.

8. A system for producing a multiple display on a cathode ray tube ofthe outputs of a pair of radio pulse echo systems having outputsoccurring in pulse to pulse alternation, comprising a pair ofquadraturely acting cathode beam deflecting means for said cathode raytube, means operating on said deflecting means to shift the cathode beambetween two starting positions on the screen thereof in synchronism withthe alternation of said outputs, means generating and applying sweepvoltages to both of said deflecting means in synchronism with the pulsesof energy emitted by said pulse echo systems, means varying themagnitude of the sweep voltage applied to one of said deflecting meansas a function of the orientation of the beam of the output producingpulse echo system, and means operable upon said cathode ray tube to clipnormally overlapping portions of the displays forming said multipledisplay, said clipping means comprising a channel to which said sweepvoltage applied to one of said deflecting means is applied, means insaid channel blocking alternate excursions of said sweep voltage, meansclipping the remaining excursions of said sweep voltage at a selectedlevel, means deriving from said clipped voltage a square waveform theexcursions of which have leading edges occurring at the time whentheexcursions of said sweep voltage reach said selected voltage level, andmeans applying said square waveform to said cathode ray tube in a mannerto blank the cathode ray beam of said tube for the duration of each ofsaid excursions thereof.

References Cited in the file of this patent UNITED STATES PATENTS

